In the late 80s I lived in an apartment building in Lansdowne, Pa (Philthydelphia). Residents had assigned parking in the lot, and on-street parking was scant.
Our assigned spot was the first in the lot after turning off the street, making it the spot people would pull into if they were visiting a resident or making a delivery. The lot had signage about no parking, towing, etc.
At least every other week I’d return from classes to find a car in my spot. I’d call the building management, they’d apologize, and 5 minutes later a tow truck would haul off the illegally parked vehicle. The tow truck driver was very friendly, and explained how towing was a bigger money-maker than gas sales or auto repairs. His dream was to move to downtown and get a rush-hour tow job. These were the dudes who made the big money, hauling in one car after another during rush hour no parking.
Are you asking if the property owners will tow off of their property during hours that they are not there? I would say its unlikely.
In the case of a strip mall, the owners are most likely some sort of property management group. They will rarely be around and will probably only act upon complaints by their tenants about long term problems. The signs are mostly for show.
Yes but pirate towers will cruise parking lots looking for such violations and will tow you - even if you are entitled to use the spot (like an employee working late).
From what I’m seeing in the answers - While a property owner can have anything towed off their property, they may end up paying the cost. The rules generally seem to be that the signage must “look like” real traffic signs. Hard to read, handwritten, etc. risk being tossed as “not obvious” by the court, leaving the land-owner to pay for the tow.
We have over the decades certain expectations of what traffic signs should look like (I.e. 15mph speed limit signs in parking lots look just like real speed limit signs; ditto stop signs). You might get some guy towed no problem if he parked on your front lawn, but if it’s a publicly accessible parking lot, if you want to restrict it, you should CYA with a valid, reasonable sign. (So much of court stuff comes back to “reasonable”. What would the average but thinking human make of this situation?) As quoted above, some jurisdictions make this explicit as to how the sign must look.
Handicapped is a special case, since they have appeared in the last few decades. The legislation requiring reserved spots tends to explicitly state how many there must be, how they need to be marked, what you need on the car to use them, etc. Since the majority are on private property, the laws were generally written to account for this. (IIRC in my area of Canada, they need both a painted symbol on the spot itself plus signage in front for when dirt or snow obscure the symbol.)
I once visited a small, boutiquey shopping center that had signs with a picture of a turtle in sneakers, and stating “Speed limit 6 1/2 mph.” I don’t think they ever tried to enforce that limit, but it got your attention in a funny way and might’ve slowed some people down.